Nigella's most challenging performance

It will be the most challenging performance of her life. On Wednesday, Nigella Lawson will appear in court in the case against her former employees, Elisabetta and Francesca Grillo, who are accused of stealing almost £700,000.

Although she is appearing as a witness for the prosecution, friends believe that, in effect, it is Nigella who is on trial as she battles to clear her name and save her career.

And she is determined to put up a fight. Contrary to reports that she might move to America, Nigella has resolved to stay in Britain and has been looking for a house in Primrose Hill, North London.

She has also maintained an unfaltering online presence, posting a recipe for 'holiday hotcakes' and mobilising 'team Nigella'. Thousands of people have shown their support for the TV chef, including Stephen Fry, DJ Lauren Laverne and Claudia Winkleman.

Meanwhile, her friends are furious that, to all intents and purposes, it appears she is in the dock alongside the Grillos.

One friend who speaks to Nigella every day told The Mail on Sunday: "It has turned into the Nigella Lawson trial. It is supposed to be about the women, not her. It is unfortunate to say the least."

The Grillo sisters have mounted a defence arguing they did not steal money from Nigella and her ex-husband, Charles Saatchi, 70. The accused pair claim they were allowed access to credit cards in return for covering up Nigella's use of cocaine, cannabis and prescription drugs.

Last week, the jury at Isleworth Crown Court was read an email Saatchi sent to his ex-wife in which he dubbed her 'Higella' and claimed she was "off her head" on drugs.

Despite saying he had "no proof" Nigella had ever taken drugs, the damage was done.

The sensational claims were broadcast around the world and the internet was awash with comment and disbelief.

The friend said: "It is hard to describe how she is. She just has to get on with the situation she finds herself in. It is very difficult. She is up and down. Now she has to just get through it."

Nigella returned to Britain at the beginning of October after filming the second series of her successful American show The Taste, which is a cross between MasterChef and The Voice.

Saatchi has continued to dine out, often at the Mayfair restaurant Scott's, the scene of the infamous 'strangling row' involving the pair in June. Nigella prefers to have people over to supper at the mews house she is renting in Central London.

Earlier this month, she made a rare outing, attending the 55th birthday party of Vogue editor Alexandra Shulman. One guest said: "She was charming but kept herself to herself for much of the night, smoking and drinking Diet Coke."

The ordeal has inevitably taken its toll on Nigella, whose father Nigel Lawson was Chancellor of the Exchequer under Margaret Thatcher and whose brother Dominic is a former editor of the Sunday Telegraph.

Another friend admitted: "Nigella is trying to put on a brave face but she's completely strung out by all this. She is looking at her life - especially her carefully constructed career - crumbling before her eyes.

"She's worried that the publicity over the trial might mean poor ratings for her new Channel 4 series - the English version of the American format - and it might be cancelled."

Despite the undoubted ordeal that lies ahead, one friend said: "There has been no hysterical response to any of this. She has kept a dignified silence.

"And there are lots of exciting projects ahead. Next year there will be her new show and Random House [Nigella's UK publisher] will be republishing her back catalogue. Nigella will be doing exactly what she does best, and what she is known for."